TACHYON HAIR ON 2-DIMENSIONAL BLACK-HOLES

Static black holes in two-dimensional string theory can carry tachyon hair. Configurations which are nonsingular at the event horizon have a nonvanishing asymptotic energy density. Such solutions can be smoothl y extended through the event horizon and have a nonvanishing energy fl ux emerging from the past singularity. Dynamical processes will not ch ange the amount of tachyon hair on a black hole. In particular, there will be no tachyon hair on a black hole formed in gravitational collap se if the initial geometry is the linear dilaton vacuum. There also ex ist static solutions with a finite total energy, which have singular e vent horizons. Simple dynamical arguments suggest that black holes for med in gravitational collapse will not have tachyon hair of this type.